Fish herbivory as key ecological function in a heavily degraded coral reef system : Fish Herbivory in Degraded Coral Reefs

Phase-shifts from one persistent assemblage of species to another have become increasingly commonplace on coral reefs and in many other ecosystems due to escalating human impacts. Coral reef science, monitoring and global assessments have focused mainly on producing detailed descriptions of reef decline, and continue to pay insufficient attention to the underlying processes causing degradation. A more productive way forward is to harness new theoretical insights and empirical information on why some reefs degrade and others do not. Learning how to avoid undesirable phase-shifts, and how to reverse them when they occur, requires an urgent reform of scientific approaches, policies, governance structures and coral reef management. Copyright © 2010 Elsevier Ltd. All rights reserved.

The world's coral reefs are in decline, with many exhibiting a phase shift from coral to macroalgal dominance . This change is often associated with habitat loss and overharvesting of herbivorous fishes, particularly parrotfishes and surgeonfishes . The challenge is to reverse this decline and enhance the resilience of coral-reef ecosystems . We demonstrate, by using a large-scale experimentally induced phase shift, that the rapid reversal from a macroalgal-dominated to a coral- and epilithic algal-dominated state was not a result of herbivory by parrotfishes or surgeonfishes. Surprisingly, phase-shift reversal was primarily driven by a single batfish species (Platax pinnatus), a fish previously regarded as an invertebrate feeder. The 43 herbivorous fishes in the local fauna played only a minor role, suggesting that biodiversity may not offer the protection we hoped for in complex ecosystems. Our findings highlight the dangers faced by coral reefs and other threatened complex ecosystems: Species or functional groups that prevent phase shifts may not be able to reverse phase shifts once they occur. Nevertheless, reversal is possible. The critical issue is to identify and protect those groups that underpin the resilience and regeneration of complex ecosystems.